Ants, of all things, could hold key to future Lake Tahoe clarity efforts

11/14/2007 8:00:00 AM

Ants are often considered nuisances, pests that are to be quickly eradicated and forgotten.

Yet, according to a team of scientists that includes Monte Sanford, a Ph.D. student, and Dennis Murphy, a professor in the Biology Department at the University of Nevada, Reno, ants could hold important keys to improving water clarity at Lake Tahoe and in maintaining ecological health in the Lake Tahoe basin.

Sanford says that one of the more common types of ants at Tahoe, "aerator ants" -- which are ant species that construct nests and extensive tunnel networks in the ground -- "can play a substantial role in facilitating water infiltration in forests, which can affect the clarity of the lake's waters."

"The study reminds us that we tend to overlook the little things that run the world," Murphy said.

The ants' contribution is simple, but important.

Sanford and Murphy, along with researchers from the U.S. Forest Service's Pacific Southwest Research Station and the University of California at Davis, studied responses of ant communities to urban development in the Lake Tahoe basin.

The abundance of aerator ants was found to drop precipitously in forests with the greatest amounts of surrounding urban land development, thus greatly reducing the likelihood that water is infiltrated into the ground, increasing the likelihood of sediment runoff, and impacting the lake's legendary clarity.

Murphy said that aerator ants can survive some nearby development, "but apparently not intensive development."

"In fact, we observed reduced numbers of aerator ants in both wildland sites and high development sites, but the ants really dropped out of the picture in areas with high levels of urban development," Sanford said.

"The responses of these aerator ants show some flexibility to respond to the pressures exerted by urban development, but that flexibility, in the form of shifts in abundance and dominance of certain species, only lasts so long" Sanford added. "At higher levels of land development, aerator ant colonies and the ecosystem services that they provide really collapse."

"It is a fine balance," Murphy said. "Our findings show that some environmental disturbances caused by human activities may in fact help these ants. We actually found increases in ant species richness and abundance in forest patches with intermediate levels of disturbance. If ants can benefit from some level of disturbance, then perhaps the notion of purchasing lots and leaving them as unmanaged 'buffer' spaces between urban and wildland areas can be looked at a bit more closely."

According to Sanford, the increase in ant diversity and abundance of aerator ants from wildland areas to forests with moderate development levels appears to be partly attributable to the removal of the often very large amounts of dead woody debris found in Tahoe's forests.

"Removing some downed wood opens up the forest floor and provides areas for aerator ants and other species," Sanford said. "Our research is important especially given the management focus at Lake Tahoe -- Tahoe's forests now more than ever are predominantly managed to reduce wildfire risk, with intensive ongoing efforts to reduce downed woody debris, an action that can benefit the aerator ants to certain point." But the research team also found that exotic, weedy plant invasions tend to increase in areas with dead wood removed. Those exotics can have a strong negative impact on these ants, indicating that exotic plants may be offsetting the positive side of fuels reductions on the ants.

"This is evidence that the whole ecosystem in the Tahoe basin is changing from urban development, fuels reductions, and exotic plants," Stanford said, "and that's reason for substantial concern.""Balancing management actions that contribute to enhancing Lake Tahoe's legendary water clarity, while reducing fire hazards in the basin will require something of a "Goldilocks strategy," Murphy said.

"A forest dense with fuels is at great risk of fire, but a forest stripped of all of those fuels losses the ants that contribute to that highly desirable blue lake," he said. Finding that "just right" forest condition in between is an immediate challenge to the basin's management agencies, Murphy added.

Critical to the success of the study, Murphy said, was the fact that the research team took a sophisticated approach to its work, studying many dozens of forested locations in the Tahoe basin, which varied from highly urbanized to essentially wild, and a wide diversity of conditions in between.

Many of those sites were once private lots that were purchased from willing sellers as part of federal and state programs to reduce the land development that has contributed to reduction in Lake Tahoe's clarity.

"Here is a case where a seemingly minor element in a complex ecosystem must be sustained to help us meet the broader environmental goals of maintaining healthy forests and a blue lake," Murphy said. "Our research suggests that ant communities and their ecosystem services should be an important target in land-use planning and conservation efforts at Lake Tahoe."